1. Field of the Invention
The present invention relates to shift rail detent mechanisms for providing a selectively variable resistance to axial or rotational movement of a shift rail for minimizing the occurrence of jumpout. In a particular preferred embodiment, the present invention relates to such a detent mechanism for a lever-shifted transmission system having means to determine a driver intent to initiate or continue a lever shift and, upon sensing such an intent, to cause the detent mechanism to provide a decreased resistance to shift rail movement.
2. Description of the Prior Art
Manually shifted vehicular transmissions of the simple and/or compound types and of the synchronized, blocked and/or non-synchronized types are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,000,060 and 5,390,561, the disclosures of which are incorporated herein by reference.
The prior art manually shifted transmissions, especially as utilized for heavy-duty vehicles such as straight trucks and conventional (i.e., not cab-over-engine) tractor/semi-trailers, utilized a manually manipulated shift lever extending upwardly from a shift tower subassembly mounted directly on the transmission housing and interacted with a multiple-rail or single shift shaft shifting mechanism of the types shown in U.S. Pat. Nos. 4,455,883; 4,550,627; 4,920,815 and 5,272,931, the disclosures of which are incorporated herein by reference.
While such transmissions are widely used and commercially successful, they are not totally satisfactory, as under certain severe road conditions, the transmissions may experience shift lever-induced jumpout (i.e., unintended disengagement of a gear ratio). This situation usually is associated with transmissions utilized in relatively heavy-duty vehicles (i e., such as MVMA Class 5 and larger vehicles), which tend to have relatively long shift levers having relatively large shift knobs, often including master valving for controlling range and/or splitter shifts, at the ends thereof.
As is known in the prior art, shift rail detent mechanisms are used to maintain the shift rails in a fixed position to resist jumpout, such as shift lever-induced jumpout. Examples of such detent mechanisms may be seen by reference to U.S. Pat. Nos. 4,550,627; 4,614,126; 4,920,815; 5,000,060 and 5,350,561, the disclosures of which are incorporated herein by reference. Shift lever detents are also useful to maintain a transmission in neutral when the engine is left running to keep the heater operational. Such mechanisms are not totally satisfactory, as the magnitude of resistance to shift rail movement needed to provide a significant resistance to jumpout or to resist accidental shifting from neutral, often objectionably increased the operator effort associated with a lever shift.
Partially automated mechanical transmission systems providing automatic assistance, such as automatic engine fuel control, for manual lever-shifted transmissions are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,593,580; 5,569,115; 5,571,059; 5,573,477 and 5,582,558, the disclosures of which are incorporated herein by reference, and to co-pending U.S. Ser. Nos. 08/649,829 now U.S. Pat. No. 5,682,790, 08/649,830 now U.S. Pat. No. 5,735,771, 08/649,831, now abandoned, and 08/666,164, all assigned to EATON CORPORATION, the assignee of this application. These systems utilize automatic engine fueling controls and/or range and/or splitter shift actuators, actuated by a driver indication of an intent to shift, allowing an old gear to be disengaged and a new or target gear to be engaged without requiring the driver to manipulate the clutch pedal (required only for vehicle launch and stop) or the throttle pedal.